The tip is 3/8". The size describes the size of the rod that the tip was designed for. The 3/8" tip works with both the 3/8" round rod and the 3/8" hex rod.
Standard Tip for Smart Stick/Mighty Probe (3/8")
TT Tools
All tips are made of high strength alloy steel and are heat-treated for added durability. Tapered edges make penetration and withdrawal easier.
The actual size of the tips is a little larger than the shaft. This allows the tip to create a clearance hole so the rod will not drag against the ground.